1. Field of the Invention
This invention relates generally to gas sampling valves and, more particularly, to a gas sampling valve for sampling gas in an engine or a combustion system so as to perform local composition measurement.
2. Discussion of the Background
A gas sampling technique is known as a means for measuring the concentration of local gases, or the air excess ratio .lambda. or air fuel ratio of an air-fuel mixture in a cylinder of an internal combustion engine or in a combustion system. This gas sampling technique is used to measure the distribution of the excess air ratio of an air-fuel mixture directly relating to exhaust components including No.sub.x, HC and soot in order to improve the performance of engines such as gasoline and diesel engines. In an example of this gas sampling technique such as the one disclosed in SAE Paper 750849, an electromagnetic drive type of gas sampling valve having a gas sampling inlet faced to a combustion chamber is mounted on a cylinder head of an engine, and the gas sampling inlet of the gas sampling valve is opened in synchronization with the rotation of the engine by a predetermined crank angle, thereby taking a small quantity of gas out of the combustion chamber. This small quantity of gas taken out by the gas sampling valve is supplied to a gas analyzer such as gas chromatography directly or indirectly after being stored in a storage vessel, and is thereby analyzed.
In this case, the measurement of the air excess ratio and combustion efficiency is possible only after the measurement and analysis of all of various components in the gas.
SAE Paper 850044 shows the technique of measuring only the air excess ratio based on the concentration of CO.sub.2 after burning the gas using a catalyst. This method, however, needs a large quantity of gas and thus needs a device for storing such gas. Further, great care must be taken in exchanging or sealing the gas to maintain measurement accuracy. Furthermore, the analyzed and the whole system are of a large size.
Thus, in the above-mentioned conventional techniques, the gas sampling and the analysis cannot be performed simultaneously. Further, in these conventional gas sampling techniques, measurement of gas is performed chiefly with respect to targeted gases in order to fully analyze gases in cylinders of an engine. Even in the case of measurement for simply determining the air excess ratio, a large amount of sampled gas is needed and the gas sampling operation must be repeated over several tens to several thousands of cycles. There are therefore problems of time lag between sampling and analysis and durability of the gas sampling valve. Moreover, in the process of transferring the sampled gas by means of the storage vessel or transference pipe, there is a possibility of external air entering the gas if the gas leaks. There is thus a problem of difficulty in the accuracy of analysis.
As mentioned above, measurement of local air excess ratio is important in the study of engines. However, the above-described gas sampling technique requires a long time for analysis and is defective in terms of accuracy. It also requires a high-cost gas analyzer which needs to be operated with a complicated analyzing technique. Therefore, these gas sampling techniques are not generally used.